hi LR
trying to better understand your workflow: is the requirement to merge all meshes from a shape only motivated to have a simple way to assign the attributes from the csv file? or is this actually a requirement of unity itself?
one reason i am asking is that by merging all meshes you have potentially a mesh with multiple materials which might also have undesired consequences...
you could also assign the attributes to all sub-meshes individually, right?
best,
simon